In the related art, there are known memory systems called solid state drives (SSDs). SSDs are devices in which nonvolatile semiconductor memories such as NAND flash memory are used.
In NAND flash memory, data may not be overwritten. Before writing to the same location in NAND flash memory, the location needs to be first erased. The NAND flash memory executes erasing in units of blocks. Therefore, in SSDs, blocks having free regions are generated by executing a relocating process called garbage collection. Sometimes, garbage collection is executed when data is transmitted from a host to be written in the NAND flash memory. As a result, garbage collection degrades write performance of a memory system.